Method of rendering cellulosic material non-adherent and article produced thereby



METHOD OF RENDERIVG CELLULOSIC MATE L NON-ADHERENT AND ARTICLE PRO- DUCED TEEREBY Francis G. A. de Monterrey, Troy, and Michael 'J. Zurlo,

Mechanicville, N.Y., assignors to General Electric Company, a corporation of New York No Drawing. Filed Mar. 26, 15953, Ser. No. 723,963

4 Claims. (Cl. 117-143) This invention is concerned with. rendering cellulosic materials non-adherent to various organic solids. More particularly, the invention is concerned with a process for rendering paper or paperboard non-adherent to normally adherent materials such as, for instance, asphalts, bitumen, tars, waxes, paraffin solids, flour-containing pastes and frozen foodstuffs, and other high molecular weight polymers, which process comprises treating the said cellulosic material with an aqueous emulsion comprising (1) a linear .polydimethylsiloxane containing terminal silicon-bonded hydroxy groups, (2) a methylpolysiloxane resin having a ratio of from 1.05 to 1.4 methyl groups per silicon atom, 3) polyvinyl alcohol as an emulsifying agent, and (4) dibutyl tin dilaurate, there being employed on a weight basis from 2 to 6 parts of the linear polydimethylsiloxane per part methyl-polysiloxane resin.

Cellulosic fibers in the form of cellulosic papers and paperboard are used extensivelyas confining and shipping means for various highly adhesive materials including such organic compositions as asphalt or pitch, tar, various unvulcanized rubbers, particularly synthetic rubbers, other high molecular weight organicpolymers usedas adhesives, etc. For optimum use of these cellulosic containers, it is essential that they be capable of being readily separated or stripped from the cargo contained therein. Thus, in the transportation and shipment of asphalt used for roofing purposes, the asphalt is generally poured while still hot intoa container, such as a carton, bag or drum whose sides are cellulosic in nature. After cooling, the asphalt becomes quite hard and can be readily transported with little difficulty. At its destination of use, it is essential that this paper in whatever form be capable of being readily stripped from the asphalt so as to permit easy access to the latter without any extraneous portions of the paper or fibers thereof adhering to the asphalt so as to undesirably affect the constitution of the asphalt.

Various treatments have been accorded these types of papers which are often referred to as anti-blocking paper (or release paper). One method for treating the paper to render it anti blocking comprises treating the paper in a three-coat operation with (1) finely divided clay and casein, (2)-finely divided clay, and (3) polyvinyl acetate. Such paper-provides release by fracture of the clay coating, but the polyvinyl acetate remains on the adhesive material. Another method commonly employed in the art involves applying several thicknesses of polyethylene tothe paper, usually by treatting the latter with solutions of the polyethylene. A still further method for treating cellulosic material to render it non-adherent, particularly to asphalt and to permit it to be readily removed from direct contact with the latter, involves depositing a doublecoating of cellulosic materials, the first coating being of clay. andthe second coating being of methyl cellulose and starch.

However, all the foregoing methods have; been exceedingly expensive and in many respects have not, been I too satisfactory since too often ithas been found that Patented May 23, 1961 2. these adhesive materials, particularly asphalt, which apparently has a high affinity for cellulosic fibers, stick to the anti-blocking paper so that great difficulty is encountered in attempting to separate the latter from the asphalt.

U.S. Patent 2,588,367 describes the use of methyl hydrogen polysiloxanes in combination with water-soluble cellulose ethers for the purpose of treating anti-blocking paper to render it less adherent to ordinarily adhesive organic compositions. Although such combinations of ingredients are ordinarily helpful in reducing the adhesive properties of, the paper, nevertheless much is left to be desired from such treatment of the paper. Often, the release properties are unreliable and the release characteristics are not uniform throughout the surface of the paper. In addition, it is essential that, in order to obtain optimum release properties, the treated paper be aged for extended periods of time, e.g., by storage before it is useful for release purposes; this is necessary because accelerated aging by high temperature treatment is not usually available commercially in paper-treating establishments. Furthermore, paper such as parchment paper cannot be heated about C. without deleteriously affecting the paper. Moreover, after treatment of paper with the methyl hydrogen polysiloxane, the abhesive characteristics (i.e., the release properties) tend to decrease with time so that after long term storage, such treated paper no longer shows abhesive characteristics. Additionally, the treating baths containing the methyl hydrogen polysiloxane tend to cure too rapidly, gumming up rolls and other equipment used in the treatment of paper for abhesive purposes.

In addition to the 'difliculties described above, particularly when using methylpolysiloxanes for anti-adhesion (abhesive) purposes, and. even when using the more currently employed methyl hydrogen polysiloxanes for this purpose, it, has been foundthat although release properties are improved, nevertheless, there is an'undesirable tendency of the silicone in the abhesive paper to migrate to the surface of the paper thereby coming in contact with the material which it is desired to release. Often the abhesive paper is in contact with compositions which are destined to be used for adhesion applications, and the tack or the adhesion is undesirably reduced as a result of this migration of the organopolysiloxane from the treated release paper to the adhesive.

Unexpectedly, we have discovered that a certain aqueous emulsion of a mixture of ingredients can be used to treat release paper, and paper treated in this manner obviates the various difliculties recited above. What is even more important, release paper treated with these compositions shows no evidence of migration of the organopolysiloxane.therein to the surface undesirablyto contaminate the material with which the release paper may come in contact. The emulsioncompositions which we have found to be so eminently suitable in the practice of the present invention comprise (l) a linear polydimethylsiloxane having terminal silicon-bonded hydroxyl groups, (2) a methyl-polysiloxane of the type recited above, (3) polyvinyl alcohol as an emulsifying agent, and (4) dibutyl tin dilaurate as the catalyst.

The hydroxy chain-stopped polydimethylsiloxanes employed in the practice of thepresent invention arethose having the general formula Ll l Where n is aninteger greater than 1, for instance, from 10 to 100,000. These polydimethylsiloxanes containing terminal silicon-bonded .hydroxyl groups (hereinafter reof siloxane unitsin the methylpolysiloxane ferred to as polydimethylsiloxane), are soluble in organic solvents such as xylene, toluene, trichloroethylene, etc., and are preferably of a fluid nature which may range in viscosity from highly fluid materials to diflicultly flowable compositions; the viscosities of such polydimethylsiloxanes may range from about to 2,000,000 centipoises when measured at 25 C.

These polydimethylsiloxanes may be prepared by any one of several well-known methods. When making the highly viscous polydimethylsiloxanes, such compositions may be obtained by hydrolyzing dimethyldichlorosilane with Water and thereafter condensing the hydrolysis product with either acidic or alkaline catalysts such as hydrochloric acid, sulfuric acid, potassium hydroxide, etc. Alternatively, one may heat cyclic polymers of the formula where m is an integer equal to from 3 to 6, for instance, octamethylcyclotetrasiloxane, with an alkaline catalyst such as potassium hydroxide, cesium hydroxide, etc (in an amount equal, by weight, to from about 0.001 to 0.1 percent based on the Weight of the octamethylcyclotetrasiloxane) at temperatures of from 125 to 175 C. for times ranging from about minutes to 2 hours or more and thereafter, if desired, removing or neutralizing the alkaline catalyst to yield a polydimethylsiloxane of Formula I having a viscosity of from about 700,000 to 2,000,000 centipoises when measured at 25 C.

When lower viscosity polydimethylsiloxanes containing terminal silicon-bonded hydroxyl groups are desired, one can treat the high molecular weight products obtained above with Water to reduce the viscosity of the polymer to within the range from about 10 to 100,000 centipoises at 25 C. This can be accomplished by blowing steam across the surface of the high molecular Weight product or through the polymer for a sufficient time to give the lower viscosity material having the desired silanol content. Such compositions and various methods for pre paring the same are more particularly described in U.S. Patent 2,607,792 and in British Patent 791,370. The use of steam in this fashion will cause a decrease in the viscosity of the polymer while at the same time the formed linear polysiloxane will have terminal silicon-bonded hydroxy groups.

An alternative method for making the linear organopolysiloxane containing terminal silicon-bonded hydroxy groups comprises adding Water to the high molecular weight polymer described in such amount that when heated at elevated temperatures, for instance, 150 to 170 C., the viscosity is reduced to the desired level of 10 to 100,000 centipoises. The amount of water used will vary depending upon such factors as the molecular weight of the polymer being treated, the time and temperature at which the mixture of high molecular weight organopolysiloxane and water will be heated, the ultimate viscosity desired, etc.

The amount of water used to reduce the molecular weight can be readily determined. For instance, one can obtain a linear fluid methylpolysiloxane containing terminal silicon-bonded hydroxy groups and having a viscosity of from 1,000 to 3,000 centipoises at 25 C. by heating a high molecular weight methylpolysiloxane (prepared in accordance with the directions above) of about 2,000,000 centipoise viscosity, with only 0.5 percent, by weight, thereof water for about 2 hours at 150 to 170 C.

The methylpolysiloxane resins employed in the practice of the present invention are composed essentially of (CH SiO and CH SiO units, the dimethylsiloxy units comprising from 5 to 40 mol percent of the total number Stated alternatively, the methylpolysiloxane resin contains an average of about 1.05 to about 1.4 methyl groups per silicon atom. A general method for preparing these methylpolysiloxanes comprises cohydrolyzing from 5 to 40 mol percent dimethyldichlorosilane and from 60 to 95 mol percent methyltrichlorosilane. These methylpolysiloxane resins may also be considered as having the formula where x has a value of from 1.05 to 1.4. Such compositions are found disclosed and claimed in U.S. 2,258,218 assigned to the same assignee as the present invention. Advantageously, the resinous hydrolysis product is dissolved in a suitable solvent, for instance, toluene, xylene, mixtures of toluene and butanol, etc., in concentrations ranging from about 10 to 90% resin solids.

We have unexpectedly found that contrary to what might be expected, dibutyl tin dilaurate gave minimum migration of the methylpolysiloxanes (i.e., the hydroxy chain-stopped polydimethylsiloxane and the methylpolysiloxane resin) and could be used in lower concentrations than when one employed other metallic soaps.

The above essential ingredients used for treating cellulosic materials to render them abhesive in the form of a coating material which is non-migratory as far as the methylpolysiloxanes contained therein are concerned, are employed in the form of an aqueous emulsion (with or Without solvent contained therein), which can be used as a treating bath for cellulosic materials such as cellulosic sheet material, parchment paper, kraft paper, linen rag paper, rice paper, glassine, cellophane, sulfite cellulose paper and the like; as well as sheeting or boxing materials such as paperboard, cardboard, pulpboard, and pasteboard. 7

The aqueous emulsion employed in the practice of the present invention advantageously comprises, on a weight basis the following:

Methylpolysiloxane resin 1 part.

Polydimethylsiloxane 2. to 6 parts.

Water 3 to parts.

Tin as dibutyl tin dilaurate 0.05 to 10% based on the weight of the polydimethylsiloxane.

Polyvinyl alcohol 0.1 to 3% based on the weight of the entire treating emulsion.

The amount of dibutyl tin dilaurate employed will depend upon such factors as, for instance, the type of methylpolysiloxane resin and the polydirnethylsiloxane employed, the type of paper to which the treating composition will be applied, as well as the medium in which the tin salt will be used, the treating conditions including temperature and time of treatment, etc.

The actual amount of emulsifying or dispersing agent employed Will depend, for instance, upon the type of ingredients present in the treating composition, the type of emulsifying agent employed, the application intended, etc. Generally, the amount of emulsifying agent satisfactorily employed may range from about 0.1 to 3%, by weight, based on the weight of the entire aqueous treating emulsion. The amount used is not critical and persons skilled in the art will have little difiiculty in determining readily the amount which gives optimum results. It is preferable that the emulsifying agent used be one which permits the emulsion to be stable under treating conditions but is readily broken within the interstices of the paper fibers to deposit the organopolysiloxane.

One method for making the emulsion type treating compositions herein described comprises, first, dissolving the emulsifying agent, e.g., polyvinyl alcohol in water, and then adding slowly the polydimethylsiloxane and the methylpolysiloxane resin. This mixture of ingredients is thoroughly homogenized (or colloided) until the polydimethylsiloxane and methylpolysi'loxane resin are intimately dispersed throughout the water phase. This material is often referred to as a master emulsion. An

- aqueous emulsion using, for example, polyvinyl alcohol as xylene is added to the tin salt prior to its addition to the solution ofwater and polyvinyl alcohol. This tin salt mixture is also homogenized to form an emulsion and in this form is added to the master emulsion in the preparation of the treating bath. The master silicone emulsion is preferably diluted to use concentrations with an additional amount of watenprior to incorporation of the catalyst emulsion.

The procedure described above for preparing. water emulsions of the treating compositions herein described may, of course, be varied within wide limits and it is not intended that the description be limiting in any manner. The presence of small amounts of organic solvents is not precluded, and under some circumstances may be desirable. If any organic solvent is employed, it is preferable that one employ those which are easily volatilized at the temperature at which treatment of the paper will take place. The emulsion should bev kept at a relatively cool temperature, e.g., around room temperature, prior to using in order to maintain its stability.

The final treating mixture can be appliedv to the paper by any convenient means, for instance with conventional dip or roller coating equipment, by padding, spraying, knife-coating, etc.; alternatively, the emulsionmay be applied by means of a size press employed in combination with a paper machine so that the treatment of the paper is on a continuous basis taking place after the paper is formed on, for instance, a Fourdrinier machine.

Following the treatment of the cellulosic material with the emulsion or emulsion-dispersion, the material is advantageously dried by passing the treated paper over heated rolls (or cans) maintained at temperatures of about 90 C. to 175 C. for from about seconds to 3 minutes or more. The useof circulating hot air at temperatures of from 100 to 160 C. may also be used for times of from 30 seconds to 5 minutes to effect curing of the treated paper. Thisdrying step will bring out the optimum release properties of the paper without further. heat treatment. Of equal significance is the fact that these optimum release properties are immediately available without requiring aging or storage of the treated paper. Obviously, the higher the temperature, the shorter the period of exposure of the paper for removingthe water and drying the paper.

In order that those skilled in the art may better understand how the present invention may be practiced, the following examples are given by way of illustration and not by way of limitation. All parts and percents are by weight.

The polydimethylsiloxane containing terminal siliconbonded hydroxyl groups (hereinafter referred to as polydimethylsiloxane) used in the following examples had aviscosity of about 3,000 centipoises when measured at 25" C. and had a ratio of approximately two methyl groups per silicon atom. This high viscosity composition was obtained by heating octamethylcyclotetrasiloxane with about 0.001%, by weight, thereof of potassium hydroxide for about 2 to 4 hours at aboutv 145 C. until a highly viscous (about 3,000,000 centipoises) benzenesoluble product was obtained having slight flow .at room temperature. About 0.5% thereof water was added and the mixture heated for about two hours at 150 to 175 C. until a product having a viscosity of about 3,000 centipoises (when measured at 25 C.) was obtained. This material was a linear fluid polydimethyl-siloxane having terminal silicon-bonded hydroxyl groups. This material was devolatilized so as to remove all volatile polymers by heating the polydimethylsiloxane under vacuum of about mm. at 135 C. until at most there was present 1% of such volatiles.

The methylpolysiloxaneresin used in the following examples was obtained by cohydrolyzing 90 mol percent methyltrichlorosilane and 10% dimethyldichlorosilane. The resinous product thus obtained-was dissolved in toluene to. give a resinous solution containing about 34% resin solids.

In the followingtests, the release characteristics of the treated paper (parchment paper was used) were determinedby pressing (by hand) a strip of surgical adhesive tape on .the surface of the treated paper and lifting the tape from the paper; evaluation of the release was determined by assigning numerical values as follows:

0-No lifting of paper whatever 1One. edge of paper lifted up to A" 2--One edge of paper lifted A" to 1 3--One edge of paperlifted 1" to 2" 4-Paper falls off after being lifted by tape. 5-Paper shakes off after being lifted bytape 6-Paper will not shake off Migration of the silicone from the treated paper to the surface with which it came in contact was determined by observing the detackification of a surgical adhesive tape (loss of tack of the adhesive) caused by migration of the siliconefrom the surface of the paper to the adhe sive on the tape. This was accomplished by pressing (by hand) a strip of adhesive tape onto the surface of the treated paper five times in five diiferent areas. This technique greatly accelerated determination of migration because the adhesive would be expected to pull oif silicone which, if given sufficient time, might migrate of its own accord to the material with which it came in contact. Surgical adhesive tape was used because a major application of release paper is its. use as interleaving sheets wherethe treated paper is in intimate contact with adhesives and no loss of tack can be tolerated in such an application. A strip of the adhesive tape was then lifted from the paper and folded over so that the adhesive surface ,(which hadbeen in contact with the release paper) was brought into contact with itself. The pull required to separate the adhesive surface from itself (evaluated subjectively as to poor, fair, fair-good, and good tack) compared with tape which had not been in contact with release paper was used as a measure of detackification of-;the tape and thus as a measure of migration of the silicone material. The methylpolysiloxane pickup was withintherange from about 0.4% to 2%, by weight, basedon the-weight of the parchment paper which was treated in every instance in the following examples.

EXAMPLE 1 The devolatilized polydimethylsiloxane and the methylpolysiloxane resin in the form of the 34% resin solids solution were mixedtogether so that on a weight basis the former was equal to 4 parts per part of the methylpolysilox-ane resin solids. This mixture was formed into an aqueous master emulsion in which 40% of the emulsion was the mixture of these two polysiloxanes, together with an emulsifying agent of 1.26% polyvinyl alcohol (manufactured and sold by E. I. du Pont de Nemours and Company of Wilmington, Delaware, under the name of Elvanol 5-42 made by cohydrolyzing polyvinyl acetate until 86 to 89% of the latter was hydrolyzed), 7.5% xylene, and the-balance water (that is, up to the emulsion was obtained by passing the mixture of ingredients through a homogenizer-to obtain a homogeneous, creamy emulsion. A catalyst emulsion was prepared from 210 parts dibutyl tin dilaurate, 95.2 parts xylene, 6.36 parts polyvinyl alcohol, and about 327 parts water similarly as was done in making the above master emulsion. The master emulsion was then mixed with the dibutyl tin dilaurate emulsion and this mixture further diluted with water and intimately mixed to give a homogeneous emulsion treating bath in which the total weight of the polydimethylsiloxane andthe methylpolysiloxane resin in the emulsion treating composition was equal to about 10% of the total emulsion, and the dibutyl tin dilaurate in the emulsion was equal to about 1% tin in the form of dibutyl tin dilaurate. Similar treating emulsions were also prepared in which the concentration of tin as dibutyl tin dilaurate was varied up to 4% of the entire treating composition emulsion. Similar treating emulsions were also prepared in which other tin salts of organic acids were used in place of dibutyl tin dilaurate to show the advantages inherent in employing dibutyl tin dilaurate in emulsion systems of this type. Table I below shows the eifects on treated parchment paper which was immersed in each instance in the emulsion bath, the treated paper removed and passed between squeeze rolls to remove excess treating composition. Thereafter, the paper was dried by passing it over a heated cylindrical roll maintained at a temperature of 110 to 130 C. for about 3 minutes.

*In total treating bath emulsion.

e As dibutyl tin dilaurate.

b As stannous 2-ethylhcxoate.

1% zinc as zine 2-ethylhcxoate.

The inferior release and migration of the paper treated with the stannous 2-ethylhexoate and zinc Z-ethylhexoate could be improved by heating the treated paper at a temperature of about 75 C. for about 24 hours to give essentially zero release and migration. However, the dibutyl tin dilaurate catalyst permitted attainment of the optimum performance without this subsequent heating step.

Although the above example has given formulations which can advantageously be used in the practice of the present invention, the following general formulations may also be helpful in determining the relationship of the master emulsion, catalyst emulsion, and the actual treating bath emulsion. Thus, the master emulsion may generally comprise the following ingredients, by weight:

28.5 parts of the hydroxy chain-stopped polydimethylsiloxane (whether devolatilized or non-devolatilized) 1.50 parts of the methylpolysiloxane resin 1.26 parts polyvinyl alcohol (or varied as the case may 7.50 parts xylene or mineral spirits (or varied as the case may be) 61.24 parts water 100.00 parts total The dibutyl tin dilaurate emulsion may comprise the following ingredients, by weight:

70.0 parts tin as dibutyl tin dilaurate (18% tin) 30.0 parts xylene 2.1 parts polyvinyl alcohol 107.9 parts water 210.0 parts total The treating bath emulsion in general used to treat the parchment paper may comprise the following ingredients, by weight:

33.30 parts of the master silicone emulsion 0.33 part of the catalyst emulsion 66.37 parts water.

100.00 parts total 7 V 7 It will be apparent that the above relationship of ingreclients in the master emulsion, the catalyst emulsion, and the treating bath emulsion may be varied pursuant. to the modifications and variations defined in the preceding examples.

Persons skilled in the art will realize that in addition to the hydroxy chain-stopped methylpolysiloxane of the viscosities recited in the foregoing examples, other linear hydroxy chain-stopped polydimethylsiloxanes (both devolatilized and non-devolatilized) containing terminal silicon-bonded hydroxyl groups of other viscosities within the range of 10 to 2,000,000 centipoises, when measured at 25 C., can be employed without departing from the scope of the invention.

The concentration of the hydroxy chain-stopped polydimethylsiloxane, the methylpolysiloxane resin, type of methylpolysiloxane resin employed, as well as the concentration of the catalyst, polyvinyl alcohol emulsifying agent, etc., may vary within the ranges previously recited within the scope of the present invention. The concentration of the dibutyl tin dilaurate may also be varied within wide limits depending on the factors recited previously.

The amount of organopolysiloxane which is picked up by the cellulosic paper material as a result of the treatment with the emulsion of the methylpolysiloxanes depends upon such factors as the absorbency of the cellulosic material, the method of application, the concentration of methylpolysiloxanes in the emulsion, etc. Generally, the amount of methylpolysiloxane pickup ranges from about 0.1 to about 5%, or more, based on the dry weight of the cellulosic material; the preferred pickup being within the range of about 0.4 to 2% methylpolysiloxane. Obviously, larger amounts of methylpolysiloxane pickup may be employed, but generally this is not necessary and usually serves merely to increase the cost of the treatment.

Advantages of using the compositions herein described for the above specified purposes are manifold. Of particular importance is the fact that when the above combination of ingredients is applied to paper, in addition to imparting abhesive characteristics thereto, the .organopolysiloxane (that is the polydimethylsiloxane and the methylpolysiloxane resin) content in the paper is substantially non-migratory and will not atfect or be transferred to the surfaces of compositions from which the abhesive paper must be readily separated. Moreover, the abhesive characteristics of the treated paper are substantially the same even after the paper is stored for long periods of time; in contrast to this, paper treated with prior organopolysiloxane compositions used to render the paper abhesive have suffered severe losses in their abhesive properties after storage for any length of time, for instance, even after only 6 months.

Of equal significance is the fact that paper treated in accordance with our process can be employed at once for its anti-release purposes with realization of essentially optimum properties. Heretofore, organopolysiloxanes previously available on the market for the same purpose required aging, that is, storing of the treated paper for times as lnog as six weeks, in order to bring out the optimum release characteristics of the treated paper. Of considerable importance is the fact that even at high temperatures, the release characteristics are maintained at optimum levels and elevated temperatures do not destroy the release film. 1

Our invention obviates a serious problem which has existed in the past. Heretofore, it was believed that methyl hydrogen polysiloxanes were an essential ingredient to treat paper to render the latter abhesive. However, methyl hydrogen polysiloxanes tended to gas due to the presence of silicon-bonded hydrogen and this posed a serious safety and toxicity problem. In addition, the loss of hydrogen from the methyl hydrogen polysiloxane as a result of the gassing of the latter markedly reduced not only the bath life' or the storage stability of the emulsion, even before the tin catalyst was added, but more seriously reduced the bath life of any treating emulsion containing both the methyl hydrogen polysiloxane and the catalyst. Because of this instability of the methylpolysiloxane in the treating bath, it tended to form rubbery and resinous layers in the treating equipment used to treat paper, particularly in the nip between the rolls which are often used to squeeze out excess treating emulsions. Attempts to reduce this formation of rubbery or resinous coatings by lowering the catalyst level resulted in incomplete curing of the silicone polymer on the paper thus increasing to a marked extent the migration of the silicone from the paper to any objects with which it came in contact; in addition this reduction in catalyst level also resulted in poor release characteristics due to the incomplete cure.

The compositions for treating cellulosic materials herein described are readily amenable to a single-step procedure and are easily regulated and controlled for adjustable methyl polysiloxane pickup by minor variations in formations. Standard paper making or paper converting equipment is readily employed in connection with the treating operations and no precautions need be taken for any toxic materials which may be contained in the treating emul- SlOIlS.

Cellulosic materials treated as described above have a wide range of usefulness. Thus, asphalt or high molecular weight organic polymers, such as various synthetic rubbers, can be poured hot into containers fashioned from the treated paper or paperboard, and after cooling it will be found that solidified asphalt or polymer is readily and cleanly separated from container walls.

Our invention permits paper treated in accordance with our process to be substituted for various materials which have heretofore been used in contact with adhesive surfaces of electricans pressure sensitive tape, adhesive tapes used for surgical purposes, and regenerated cellulose tapes carrying a permanent adhesive upon one surface. Vulcanized or unvulcanized sheets of rubber can be prevented from adhering to each other despite the fact that these sheets of rubber are quite sticky and cohesive when in direct conttact with each other. Paper treated in accordance with the instant invention is also useful in lining various boxes of partially prebaked goods, such as buns, rolls and the like, and advantage can be taken of the outstanding release properties at elevated temperatures by completing the baking cycle in the original container in which the baked goods are purchased.

What we claim as new and desired to secure by Letters Patent of the United States is:

1. The method of rendering cellulosic fibrous sheet material non-adherent to surfaces which normally adhere thereto, which comprises treating the said material with an emulsion treating composition consisting essentially of (1) a linear polydirnethylsiloxane containing terminal silicon-bonded hydroxy groups, (2) a methylpolysiloxane resin having a ratio of from 1.05 to 1.4 methyl groups per silicon atom and composed essentially of (CH SiO and CH SiO units, (3) polyvinyl alcohol as an emulsifying agent and (4) a catalytic amount of dibutyl tin dilaurate, and thereafter drying the treated material.

2. The method for rendering cellulosic fibrous sheet material non-adherent to surfaces which normally adhere thereto, which process comprises treating the cellulosic fibrous sheet material with an emulsion treating composition consisting essentially of, by weight:

(a) 1 part of a methylpolysiloxane resin containing from 1.05 to 1.4 methyl groups per silicon atom and composed essentially of ('CH SiO and CH SiO units,

(b) from 2 to 6 parts of a linear polydimethylsiloxane containing terminal silicon-bonded hydroxy groups,

(c) from 3 to parts water,

(d) from 0.05 to 10% tin as dibutyl tin dilaurate, based on the weight of (b), and

(e) from 0.1 to 3% polyvinyl alcohol based on the weight of the entire emulsion treating composition, and thereafter drying the treated material.

3. The method as in claim 2 in which there is also present an inert organic solvent in the emulsion.

4. Cellulosic sheet material treated in accordance with the method described in claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 2,442,196 Coggeshall May 25, 1948 2,504,388 Braley Apr. 18, 1950 2,588,367 Dennett Mar. 11, 1952 2,814,601 Currie et al Nov. 26, 1957 

1. THE METHOD OF RENDERING CELLULOSIC FIBROUS SHEET MATERIAL NON-ADHERENT TO SURFACES WHICH NORMALLY ADHERE THERETO, WHICH COMPRISES TREATING THE SAID MATERIAL WITH AN EMULSION TREATING COMPOSITION CONSISTING ESSENTIALLY OF (1) A LINEAR POLYDIMETHYLSILOXANE CONTAINING TERMINAL SILICON-BONDED HYDROXY GROUPS, (2) A METHYLPOLYSILOXANE RESIN HAVING A RATIO OF FROM 1.05 TO 1.4 METHYL GROUPS PER SILICON ATOM AND COMPOSED ESSENTIALLY OF (CH3)2SIO AND CH3SIO3/2 UNITS, (3) POLYVINYL ALCOHOL AS AN EMULSIFYING AGENT AND (4) A CATALYTIC AMOUNT OF DISBUTYL TIN DILAURATE, AND THEREAFTER DRYING THE TREATED MATERIAL. 